The campaign took on a life of its own online as well, with people across the world sharing photographs on social media of themselves bearing signs saying "FreeAJStaff."
Mohamed Fahmy and his colleagues — Australian Peter Greste and Egyptian Baher Mohamed — have been behind bars since Dec. 29 and are accused of belonging to a terrorist organization and spreading false news.
Their arrests were characterized as part of a crackdown on the Muslim Brotherhood, an Islamist organization that Egypt's military-backed government has branded a terror group.
Egyptian authorities have said Al-Jazeera is biased towards the Brotherhood, an allegation the Qatar-based satellite news broadcaster has denied, saying its employees were simply going about their work.
That message — that journalism is not a crime — was at the heart of Thursday's international rallies.
In Toronto, journalists, media executives and concerned citizens gathered in a windy public square to demand Egypt drop its charges against Fahmy and his colleagues.
"They are reporters, producers, journalists and they've been put in jail for doing their jobs. It's unjust," said Tom Henheffer, executive director of the Canadian Journalists for Free Expression.
"It's crucial that we gather for one of our fellow Canadians and fight to get him out of prison."
Part of the fight is ensuring that the case is kept in the public spotlight, said John Stackhouse, the editor-in-chief of The Globe and Mail.
"Silence is deadly. We're here not only to shout out for Mohamed Fahmy, but to shout for journalism," he said at the Toronto rally.
"Journalists require free expression, whether it's in Canada or Egypt or anywhere else and none of us should take that for granted."
A similar message was broadcast in various cities around the world, where journalists and free speech advocates gathered in centres that included London's Trafalgar Square, Lebanon's Martyrs' Square and in Kenya's capital, Nairobi.
The international rallies also called for the release of Abdullah Al Shamy from Al Jazeera's Arabic channel, who has been detained in Egypt for more than six months without charge and has been on a hunger strike since January 23.
A spokeswoman from Egypt's embassy in London, however, said Thursday's rallies would have no effect on her country's prosecution of the journalists.
"There is a case in front of a court," said Sohair Younis. "We will not cancel the trial because of the protest."
The trial for Fahmy and his colleagues began last week, with all three pleading not guilty to the charges against them.
The trio are being tried as part of a group of 20 individuals who authorities say worked for Al-Jazeera. At least 12 of those are being tried in abstentia.
Fahmy needs Canada's support more than ever, said Jet Belgraver, a producer at Al Jazeera English's Toronto bureau.
"We're calling on the Canadian government to make a public statement about getting our colleagues released," she said. "We're looking at the disturbing trend that we see with regards to the deterioration of the freedom of the press in Egypt and we should all be alarmed by that."
The Department of Foreign Affairs has said senior Canadian officials have raised Fahmy's case with Egyptian authorities and have requested a fair and expeditious trial.
Fahmy's family has also noted that while consular staff in Cairo have been extremely helpful, officials have indicated the 40-year-old's dual citizenship limits how much they can do.
Nonetheless, Fahmy's brother said the family was "extremely grateful" for Thursday's show of support.
"These things definitely have an impact and generate needed pressure on Egyptian authorities," said Adel Fahmy. "They are listening, let's hope that the response is the way we want it."
Mohamed Fahmy's family moved to Canada in 1991. He lived in Montreal and Vancouver for years before eventually moving abroad for work, which included covering stories for the New York Times and CNN.
— with files from the Associated Press.